If three friends get together one with a Kindle 3, another with a Kindle DX and a third with a Kindle 2, can they all read the same electronic book? Probably not leagal for the friends to do this but is it possible? Not that one would want to.

Most DRM'd Kindle books can be shared among up to six devices. The only restriction is that they must all be registered to the same account. If the book is in the public domain, then there are no restrictions at all.

Why do you think people wouldn't want to? If you cruise some of the social networking book reader sights you will see where groups of friends do this all the time. They establish an Amazon account and everybody puts in an amount of money, usually via gift card. They then group buy the book. You temporarily de-register your Kindle from your own account, register it to the group account, and download your book. Then you move back to your own Amazon account. Most licenses restrict a Kindle book to 6 devices at one time, but a few will have a smaller number.

Especially with high Agency pricing. If a book costs $14.99 - I'd much rather share that bill with 5 of my closest friends than buy it all on my own.

Perish the thought, but you could of course strip out the DRM and convert the book to any other format you like with the freebie Calibre....

I know what you meant here, but I think it may mislead some people into thinking that Calibre is free DRM-stripping software.

Third party addons provide the functionality of which you speak, but Calibre itself has nothing to do with DRM-removal. It's just fantastic ebook library management software. Let's not give people the wrong idea.

You can enjoy your Kindle content on Kindle devices or Kindle applications that are registered to your Amazon.com account. There may be limits on the number of devices (usually six) that can simultaneously use a single book. Subscriptions to newspapers or periodicals cannot be shared on multiple devices. You can see all your Kindle content and send downloads to your registered Kindles or Kindle applications from the "Your Orders" section of the Manage Your Kindle page.

thanks for your answers.
I didn't know it till now. OK, If I understand correctly, the limitation is per book. But I can still register as many Kindle as I want. (I think, this is the main advantage for the Kindle in comparsion to other eReader and ADE.)